Recently, to achieve higher energy saving in image forming apparatuses of an electrophotographic system, there is a need for a toner for electrostatic image development (hereinafter may be referred to simply as a “toner”) that is heat-fixable at lower temperature.
To address the need for low-temperature fixability, Patent Literature 1, for example, discloses a toner containing a crystalline polyester resin as a fixing aid.
Although such a toner has good low-temperature fixability because of the sharp melting properties of the crystalline polyester resin during heat fixation, the toner has a problem in that its viscosity decreases abruptly during melting, so that the glossiness of the image becomes excessively high, causing glare.
In view of the above, Patent Literature 2, for example, proposes a toner including an amorphous portion having urethane bonds that suppresses the excessive reduction in viscosity of the crystalline polyester resin in a high-temperature state to thereby achieve high glossiness over a wide temperature range.
However, such a toner has a problem in that, although sufficient glossiness is obtained when the toner is used for printing on high-gloss paper such as coated paper, unevenness in gloss occurs when the toner is used for printing on low-gloss paper such as plain paper, so that stability of glossiness cannot be ensured for various types of paper.
For example, Patent Literature 3 proposes a toner in which the type of resin used is not a polyester resin and which includes a combination of a styrene acrylic resin composed of a styrene-based monomer and a (meth)acrylate-based monomer and a high-molecular weight styrene acrylic resin composed of specific acid monomers. In such a toner, the high-molecular weight styrene acrylic resin melts when the toner is in a high-temperature state. The elastic movement of the resins caused by a small temperature change is thereby suppressed, so that unevenness in gloss on paper sheets can be suppressed during continuous printing.
There is a description that, with such a toner, glossiness can be stabilized against temperature. However, the stability of glossiness is not ensured for various types of paper.